Effect of packing geometry on the rate of mass and heat transfer at a vertical tube imbedded in fixed bed under single and two phase flow

Abstract

Rates of liquid–solid mass transfer and heat transfer (by analogy) were studied in an annular reactor with a packed annulus. Two types of inert fixed bed packing were used namely, cylinders and Raschig rings. The electrochemical technique which involves measuring the limiting current of the cathodic reduction of ferricyanide ion in a large excess of sodium hydroxide was used in the present study. Variables studied are packing geometry, packing size, gas and liquid superficial velocities and physical properties of the solution. The presence of inert fixed bed in the annulus enhanced the rate of mass transfer and the rate of heat transfer at the outer wall of the inner cylinder by a factor ranging from 1.1 to 6.1 depending on the packing geometry, particle size and both the liquid and gas superficial velocities. The present data were compared with the previous data on the packed annulus with inert spherical packing. For single phase liquid flow the mass transfer enhancement ratio increases in the order: Raschig rings>cylinders>spheres, while in the case of two phase flow, spheres gave the highest enhancement ratio. For the present range of conditions it was found that, as the particle size decreases the enhancement ratio increases. All data were correlated in the form of dimensionless equations.Possible practical applications of the present study such as design of fixed bed reactor internal cooler, prediction of the rate of diffusion controlled corrosion of vertical tube cooler imbedded in a fixed bed reactor and design of annular double tube catalytic and electrochemical reactors with a fixed bed turbulence promoter were highlighted.